Vittek J, Gordon G G, Southren A L, Rappaport S C, Munnangi P R, Lieber C S
J Pharmacol Exp Ther. 1981 May;217(2):411-5.
The effect of ethanol on testosterone-5 alpha-A-ring reductase activity was studied in the whole homogenate and/or subcellular fractions (microsomes and cytosol) of buccal mucosa, gingiva, liver and prostate from intact ethanol-fed (36% of dietary calories were given as ethanol for up to 360 days) and pair-fed control rats. An increased enzyme activity was found in the hepatic, prostatic and gingival homogenates from ethanol-fed rats. No difference in the enzyme activity was seen in the homogenates of buccal mucosa. However, when the buccal mucosal microsomal fraction was used a significant (P less than .005) increase in the enzyme activity was found in the ethanol-fed rats. It was determined that the lack of an increase in 5 alpha-reductase activity in the buccal mucosal homogenates from ethanol-fed rats was due to the presence of a cytosolic inhibitor of this enzyme. Enzyme kinetics showed a decrease in the velocity in correlation with the increasing concentration of cytosolic inhibitor (Vmax control = 1.9 and Vmax ethanol = 1.7, 1.45 and 1.0 nmol, respectively). The apparent Km (0) and Kp (1--3) values were similar for all combinations (4.5 x 10(-5) M). In addition, a similar Ki constant (2.2 mg of cytosolic protein) was found for different testosterone concentrations. These results suggest that the ethanol-induced cytosolic inhibitor in buccal mucosa combines with the enzyme, independent of the substrate and inhibits it by an allosteric mechanism. Studies using dialysis, heating and tryptic digestion suggests that the inhibitor is a protein.
研究了乙醇对完整的经乙醇喂养（36%的膳食热量以乙醇形式提供，持续360天）和配对喂养的对照大鼠的颊黏膜、牙龈、肝脏和前列腺的全匀浆和/或亚细胞组分（微粒体和胞质溶胶）中睾酮-5α-A环还原酶活性的影响。在经乙醇喂养的大鼠的肝脏、前列腺和牙龈匀浆中发现酶活性增加。在颊黏膜匀浆中未观察到酶活性的差异。然而，当使用颊黏膜微粒体组分时，发现经乙醇喂养的大鼠的酶活性有显著（P＜0.005）增加。已确定经乙醇喂养的大鼠的颊黏膜匀浆中5α-还原酶活性缺乏增加是由于该酶的胞质溶胶抑制剂的存在。酶动力学表明，速度随着胞质溶胶抑制剂浓度的增加而降低（Vmax对照 = 1.9，Vmax乙醇 = 1.7、1.45和1.0 nmol，分别）。所有组合的表观Km(0)和Kp(1-3)值相似（4.5×10⁻⁵ M）。此外，对于不同的睾酮浓度，发现了相似的Ki常数（2.2 mg胞质溶胶蛋白）。这些结果表明，乙醇诱导的颊黏膜胞质溶胶抑制剂与该酶结合，与底物无关，并通过变构机制抑制它。使用透析、加热和胰蛋白酶消化的研究表明该抑制剂是一种蛋白质。
